1) Field of the Invention
The present invention relates to an image forming apparatus that has an engine section having a scanner, a plotter, and a CPU, connected to a controller having an integrated circuit for image processing, thereby to carry out image formation processing under the control of the CPU.
2) Description of the Related Art
Conventionally, in many cases, an image forming apparatus such as a printer or a copying machine has an engine section connected with a controller that includes an application specific IC (ASIC) for image processing and a central processing unit (CPU), and carries out an image formation processing by using this controller.
For example, in the copying machine, the ASIC that has a plurality of hardware elements for image processing is mounted on the controller, and this ASIC and the engine are connected to each other via a peripheral component interconnect (PCI) interface. A CPU and the ASIC are connected to each other. The copying machine carries out copying under the control of the CPU.
If an image forming apparatus with excellent performance is to be manufactured, the controller that executes drawing and control is replaced with a high-speed controller for each unit.
However, interfaces of conventional CPUs are made open, but interfaces of recently available reduced instructions set computer (RISC)-type general-purpose CPUs are not made open. Therefore, it is necessary to connect the ASIC with the CPU via a chip-set, which restricts the performance of the CPU.
Specifically, when the CPU is connected with an external device via the chip-set, a PCI bus is usually used. However, the PCI that passes through the chip-set has low performance. Therefore, the PCI is not suitable for structuring an image forming apparatus such as a printer and a copying machine.
Consequently, when the CPU whose interface is not made open is utilized for the controller of the image forming apparatus, how properly data is to be transferred between the chip-set of the CPU and the engine and how best to execute a high-speed image formation processing are extremely important issues.
Particularly, some of recently available multi-function machines have functions of a copying processing, a printer processing, and a facsimile processing that are not controlled by individual CPUs mounted on separate boards unlike the conventional technology, but controlled by one and the same CPU. Therefore, how to solve the reduction in performance is an extremely important issue.
Further, these multi-function machines have a function of combining a plurality of scanned image data or a plurality of image data to be printed, and outputting a combined one image data, based on the instruction from a user, at the time of forming images for a copier or a printer. When the image data combining function is executed, how to achieve a high-speed image formation processing is an extremely important issue as well.